Filleting fish requires removal of byproducts such as bones, skin, fin, scales, viscera and head. Most processors fillet fish by mechanical means. Mechanical filleting of one hundred pounds of trout (Oncorhynchus mykiss) yields approximately forty pounds of fillets and sixty pounds of byproducts. The byproducts contain approximately twenty pounds of meat, which is half the amount of the fillets, and five pounds of fish oils (lipids). The byproducts are primarily land-filled, or ground and discarded. In descriptive terms, per two truckloads of trout fillets going to the market, one truckload of trout meat and a quarter of a truckload of trout lipids, which are not recovered from the byproducts, are land-filled, or ground and discarded.
Historically fish byproducts have not been fully utilized by the rendering industry due to the “fishy odor” caused by auto-oxidation of fish oil. The odor is transferred to the meat of animals fed excessive amount of fish in their diets, resulting in lower meat quality, and thus, limited consumer acceptance. Free radicals, normally generated during the auto-oxidation, further deteriorate other components of animal feeds such as proteins, vitamins and the like. Fish processors incur expenditures to remove processing byproducts from their facilities. These byproducts are also a significant environmental bio-burden.
Mechanical filleting of other fish species yields even less fillets and more byproducts. Mechanical filleting of one hundred pounds of tilapia (Oreochromis niloticus) yields approximately thirty pounds of fillets and seventy pounds of byproducts, resulting in even higher amounts of fish meat and oil being disposed of on per fish basis. Species such as Atlantic menhaden (Brevoortia tyrannus) are regarded as low-value species due to high amounts and distribution of bone, and high concentration of lipids. Fish species that have characteristics similar to menhaden are underutilized, or not utilized, for human consumption due to the unavailability of a proper meat recovery technology that can efficiently eliminate the bones and lipids from the fillets.
Antarctic krill (Euphausia superba) are small, shrimp-like crustaceans in the seas with the largest biomass of any multi-cellular animal species on earth. Estimates state that one hundred fifty million metric tons of krill could be an annual sustainable harvest compared with one hundred million metric tons of the total global seafood human consumption. Small krill size and endogenous proteases are processing challenges, however, which have resulted in the failure of commercial krill fisheries for human consumption. According to the Food and Agricultural Organization (FAO), Atlantic and Pacific fish stocks have been exceeding the maximum sustainable levels since 1980 and 1999, respectively. Current commercial catch results in over-fishing and should be lowered to approximately eighty million metric tons. Utilization of fish meat and lipids recovered from fish filleting byproducts, krill, and species such as menhaden for human consumption would partially alleviate the environmental stress on the current marine environment.
The growth of the aquaculture industry encourages the development of technologies that recover proteins and lipids from filleting byproducts, and increases the total return. Existing surimi technology could be a good alternative for recovery of functional proteins; however, the traditional surimi processing cannot recover proteins from the byproducts and uses excessively large volumes of water. Surimi is de-boned and skinned fish; the fillets are minced, washed and finally strained to form a concentrated fish paste.
Surimi is an ancient process to make a protein food predominantly derived from fish. Water is used in the process for making surimi, and can be used in a ration from about two parts water to one part fish up to about five parts water per one part fish; typically, three parts water is used per one part fish. Two to five washes are used. Twenty to thirty percent of the fish muscle proteins are solubilized when the ground muscle is washed with water. These soluble proteins, known as sarcoplasmic proteins, are generally not recovered from the wash water of the surimi process. These solubilized proteins are a good source of protein for animal or human feedstock. Only minced proteins, typically fish muscle proteins, are used in the surimi. The resultant washed minced protein product, in solid form, is then processed further to make protein gels. Kamboko is a popular fish sausage, produced by the surimi process, in which the washed minced fish is heated until it gels. High quality surimi is generally only produced from lean white fish. About fifty to sixty percent of the total protein of the muscle tissue is lost with dark-fleshed fish sources.
Newer methods have been derived in an effort to extract edible protein from muscle sources. U.S. Pat. Nos. 6,005,073 ('073) and 6,288,216 ('216) issued to Hultin et al., on Feb. 12, 1997 and on Sep. 11, 2001 respectively, disclose a process for isolating a protein composition from a muscle source and protein composition by mixing a particulate form of the muscle with an acidic aqueous liquid having a pH below about pH 3.5 to produce a protein rich solution. A protein rich aqueous solution is separated from solids and lipids, including membrane lipids. The protein rich aqueous solution can be treated to effect protein precipitation, followed by protein recovery. Furthermore, the inventions, of the '073 and '216 patents, require frequent water replacement. The particulate form of muscle is pre-prepared from muscle that has already been separated from most bone and other byproducts.
U.S. Pat. No. 6,451,975 ('975) also issued to Hultin et al. on Sep. 17, 2002 discloses a protein composition and process for isolating a protein composition from a muscle source by mixing a particulate form of the tissue with an acidic aqueous liquid having a pH below about pH 3.5 to produce a protein rich solution substantially free of myofibrils and sarcomere tissue structure. The protein rich aqueous solution can be treated to effect protein precipitation, followed by protein recovery. U.S. Pat. No. 6,136,959 ('959) issued to Hultin et al. on Oct. 24, 2000 describes an alkaline protein extraction process which isolates edible protein from animal muscle by solubilizing the protein in an alkaline aqueous solution. The resultant solution contains 15% or less animal muscle. Again the muscle is pre-prepared from muscle that has already been separated from most bone and other byproducts.
U.S. Patent Application No. 2003/124,239 applied for by Kelleher on Feb. 19, 2003 describes a water soluble peptide composition, also derived from animal muscle tissue proteins. An enzyme is utilized in the process to make the peptide composition, and the resultant peptide composition contains less than about one weight percent fats and oils based upon the weight of the peptide composition and less than about two weight percent ash based on the weight of the peptide composition.
U.S. Patent Application No. 2004/067,551, PCT applied for by Hultin et al. on Sep. 5, 2001, describes a protein extraction process for isolating edible protein from animal muscle by solubilizing the protein in an alkaline aqueous solution. Undesirable components such as bones, neutral lipids, membrane lipids, fatty pieces, skin, cartilage, and other insoluble material are removed and discarded.
U.S. Patent Application No. 2005/233,060 applied for by Kelleher on Sep. 5, 2003 discloses a functional animal muscle protein concentrate composition and process for making the protein concentrate composition. The concentrated aqueous acidic protein solution derived from animal muscle tissue is added to the meat or fish prior to cooking. Similarly, U.S. Pat. No. 6,855,364 issued to Kelleher et al. on Feb. 15, 2005 describes a process for retaining moisture in cooked animal muscle which involves adding a dry protein mixture or an aqueous acidic protein solution derived from animal muscle tissue to meat, including fish, prior to cooking.
All of these processes take advantage of low protein solubility at their isoelectric point. It is well known in the art to use low protein solubility at their isoelectric point to isolate proteins. Furthermore, these processes produce peptides, which are products of a hydrolytic breakdown of proteins.